1. Technical Field
The present invention relates to methods and apparatus for performing analyses on whole blood samples from microscopy images in general, and to automated version of the same involving platelets in particular.
2. Background Information
Medical diagnostics often include analyses of a whole blood sample from a patient. One of the more popular diagnostics is a complete blood count (referred to as a “CBC”), which is a suite of tests that includes a “platelet count” (i.e., a thrombocyte count). The platelet count is actually a concentration determination; i.e., number of platelets per volume. In an adult, a normal platelet count is typically about 150,000 to 450,000 platelets per microliter of blood. An abnormal platelet count can be an indicator of a health problem; e.g., infection, disease, etc. If platelet levels fall below 20,000 per microliter, spontaneous bleeding may occur and is considered a life-threatening risk.
Historically, platelet counts have been performed either by smearing a small amount of undiluted blood on a slide or by flow cytometry. In the case of the smear, the sample is applied to a slide and the platelets and other constituents residing within the smear are counted. The platelet count (i.e., platelets per volume within the sample) is estimated based on the relative constituents within the sample.
To perform a platelet count via an electrical impedance or optical flow cytometer, the blood sample must be diluted and then sent through a small vessel wherein electrical impedance or optical sensors can evaluate constituent cells within the sample as they pass serially through the vessel. The accuracy of these devices can suffer, depending upon the constituents present within the sample. In an impedance counter, for example, red blood cell fragments can be construed and counted as platelets, and giant platelets can be construed and counted as red blood cells (RBCs). In both instances, the accuracy of the automated platelet count suffers. In addition, the dilution of the sample must be precise or the accuracy is negatively affected, and the diluted sample must be properly disposed of post-analysis. The internal plumbing required to handle the diluted sample often requires maintenance and at best contributes considerably to the complexity and cost of the device.
What is needed is an apparatus and method for performing automated analyses on a whole blood sample, including a platelet count, which can overcome the limitations of the prior art, including the time required to perform the analysis, the operator skill level required to perform the analysis, and one that can provide greater versatility than known prior art methods and apparatus.